A large number of microorganisms have been found to accumulate polyesters, as energy storage compounds, in the cells thereof. A typical example thereof is Poly-3-hydroxybutyrate [hereinafter simply referred to as F(3HB)], which is a homopolymer containing a monomer unit (3HB) represented by the following Formula (2). ##STR2##
P(3HB) is a so-called biodegradable plastic, which undergoes biological degradation in natural environments; however, if viewed as a polymer material, it is insufficient for practical use because it is highly crystalline, hard and brittle.
As a means for overcoming these drawbacks, it has been proposed to incorporate a monomer unit which is structurally different from 3HB to compose the polyester. The methods based on this concept can be roughly divided into two groups as follows.
(1) According to Japanese Patent Laid-Open Nos. 150393/1982, 69225/1983, 269989/1988, 48821/1989 and 156320/1989, copolymer F(3HB-CO-3HV), containing 3-hydroxyvalerate (a monomer unit represented by Formula (3), simply referred to as 3HV) and 3HB, is obtained by culturing Alcaligenes eutrophus, a microorganism which essentially produces P(3HB), from a carboxylic acid having an odd number of carbon atoms, such as propionic acid or valeric acid, as a carbon source. Similarly, it is reported that copolymer P(3HB-CO-4HB), containing 4-hydroxybutyrate (a monomer unit represented by Formula (4), simply referred to as 4HB) and 3HB, is obtained from 4-hydroxybutyric acid or .gamma.-butyrolactone, as a carbon source. ##STR3##
(2) According to Japanese Patent Laid-Open No. 226291/1988, it is reported that copolymer P(3HA), having 3-hydroxyalkanoate (simply referred to as 3HA) having 6 to 12 carbon atoms can be biosynthesized by Pseudomonas oleovorans ATCC29347, a hydrocarbon-utilizing bacterium, from alkanes. It as a carbon source. Here, to provide a clear representation of the relationship between each monomer unit structure and carbon number in 3HA, this monomer unit is referred to as a C.sub.x unit. ##STR4##
According to the above-mentioned patent publications, 3HB is a C.sub.4 unit and 3HV is a C.sub.5 unit; Pseudomonas oleovorans is capable of intracellularly synthesizing and accumulating copolymers containing C.sub.6 to C.sub.12 units.
Also, "Applied and Environmental Microbiology, 1988, pages 1977-1982" states that the carbon source alkane should have at least 6 carbon atoms for Pseudomonas oleovorans to synthesize a polyester, and that units exceeding C.sub.12 are not synthesized even if an alkane having a carbon number of 12 or more is added.
As stated above, two types of copolymer have been proposed. The copolymers of type 1 have a few methylene groups in the side chain thereof, and they are physically plastic-like polymers. The copolymers of type 2 have a large number of methylene groups in the side chain thereof, and they are physically gel-like polymers. The latter copolymers of type 2 have not been found practically valuable because their melting point (Tm) is about 40 to 60.degree. C., which is too low to retain hardness.
The present inventors have conducted investigations in search of a microorganism which utilizes long-chain fatty acids having 14 to 22 carbon atoms or triglycerides comprising such long-chain fatty acids and which accumulates a polyester in the cells thereof, and have found a bacterial strain which accumulates a random polymer having extremely long chains of methylene groups (up to C.sub.16 units) in the side chain thereof and also having a double bond in the side chain thereof. The present inventors have made further investigations based on this finding, and thus developed the present invention.